The present application relates to ceramic dental devices, such as dental crowns, veneers, bridges, implants, or dentures, and processes and materials used for making dental devices containing ceramics.
One method for the manufacture of ceramic dental devices involves providing a green-state or partially sintered dental blank that is first shaped, for example by CAD/CAM milling, and then sintered at a high temperature to produce a final dental device. Typically, such green-state material is partially sintered to form a bisque-state material that is hard enough to retain its structure while being milled, yet soft enough to allow relatively rapid shaping that does not damage the milling tool.
Such a green-state material may contain ceramic particles mixed with a binder that evaporates during the formation of the bisque-state material, leaving pores between the ceramic crystals of the bisque-state material. During solid state sintering, a reduction of free energy occurs, which is a driving force in reducing the pore size, so that the final sintered product has a shape that replicates the milled bisque-state or green-state intermediate product but is reduced in size.
One way to quantify the overall amount of pores that exist in an intermediate or final product is to measure the density of that product, as compared to a theoretical density of a ceramic material that is to form the final product, assuming that product is pore-free. Typical green-state or bisque-state materials may have a relative density that is between fifty-percent and eighty-percent, although it should be noted that in the case of green state materials the relative density includes a non-ceramic binder as well as ceramic particles, compared to the theoretical pore-free density of the final product ceramic material.
The ceramic particles that are used in the green state material may be manufactured by hydrolyzing an aqueous metal salt solution, such as a solution of zirconia, to obtain hydrous zirconia sol having an average particle size of from 0.05 to 0.3 micron. This zirconia sol can then be mixed for example with an yttrium compound, after which the mixture is calcined at a temperature ranging from 800° C. to 1100° C., followed by ball milling the calcined matter. The crystallite grains produced by this process may have a size as small as ten nanometers, but are not present individually but rather agglomerated during hydrolysis and calcining, which sinters the particles at elevated temperatures. Even after ball milling to break up the agglomerated particles, the particle size is at least about double the crystallite size, and typically greater than twenty nanometers, while some of the particles that make up the powder commonly exceed one hundred nanometers.
U.S. Published Application No. 2009/0321971 to Brodkin et al. teaches that the widely divergent size of the particles that form such a ceramic powder is advantageous for hand-built dental restorations as well as for feedstock for CAD/CAM restorations. As also noted in that application, although pore size is reduced during sintering, the pores typically are not completely removed, so that a final product such as a dental crown or other prosthesis may contain a multitude of microscopic pores. The pores may reflect light to an extent that for some dental ceramics the prosthesis has lower translucence than a natural tooth.
As noted in U.S. Pat. No. 4,520,114 to David, ball milling induces a stress that transforms tetragonal zirconia, which has good strength and resistance to cracking, to a monoclinic phase crystal structure, which has lower strength and much lower resistance to cracking. As the ball milling breaks large particles into smaller particles, the most complete transformation away from tetragonal zirconia occurs on particle surfaces that are created by the breaking. In addition, the surface portions of large particles are most directly affected by the pressure of the ball milling even without breakage, and for this reason also the surface portions are the most completely transformed from tetragonal zirconia to monoclinic zirconia.
Thus, the transformation to monoclinic phase zirconia becomes more complete as the particles are made smaller and the surface portions extend throughout the particles. The zirconia particles described in David are significantly larger than those of Brodkin et al., and for the reasons mentioned above, zirconia particles produced by hydrolysis, calcining and ball milling may have little or no tetragonal zirconia when the particle size is significantly less than fifty nanometers. Such a transformation to monoclinic phase zirconia is not reversed in bisque-state zirconia, and is only partly reversed at typical sintering temperatures of 1000° C.-1200° C. Tetragonal zirconia has high flexural strength, as mentioned above, because it resists crack propagation by transforming to monoclinic zirconia due to stress induced by a crack, absorbing energy and changing the crystal lattice along which the crack would otherwise propagate.
Instead of producing dental ceramic powder by the conventional “top-down” approach of hydrolysis, calcining and ball milling, the present inventors have employed a “bottom-up” approach of producing dental ceramic crystals as individual nanoscale particles that do not need to be broken down. The dental ceramic particles created by this approach can be made much smaller than is conventional, and issues such as transformation of the particles from tetragonal zirconia to monoclinic zirconia are avoided. The dental ceramic particles created by this approach can also be more uniform in both shape and size distribution. Cylindrical and spherical particles can be manufactured by this approach, whereas the prior art dental ceramic particles were generally neither. In addition, the smaller size of the tetragonal zirconia particles increases optical translucence by reducing scattering from birefringence, and the small average size and tight distribution of sizes can essentially eliminate pores in a sintered product. Various dental ceramic particles and powders can be made by this approach, in addition to tetragonal zirconia.
In one embodiment, dental ceramic particles are created as a vapor of the particles which is then collected as a powder. In one embodiment, dental ceramic particles are created by vaporization of solid ceramic bodies. In one embodiment, dental ceramic particles are created by vaporization and/or ionization of solid metal bodies, and the subsequent reaction of vaporized metal atoms and/or ions with oxygen, nitrogen and/or carbon atoms or molecules containing such atoms.
In one embodiment, ultrafine dental ceramic particles are created by a chemical vapor synthesis (CVS) system. In one embodiment, ultrafine dental ceramic particles are created by a physical vapor synthesis (PVS) system. In one embodiment, ultrafine dental ceramic particles are created by a combined CVS and PVS system. In one embodiment, ultrafine dental ceramic particles are created by an arc in liquid system.
In one embodiment, a dental device is disclosed comprising a solid body made of dental ceramic molecules including at least eighty mass percent crystals having a mean size of between one nanometer and one hundred nanometers, and a standard deviation from the mean size that is less than twenty percent of the mean size, the body having a shape of a dental prosthesis, having a flexural strength that is between six hundred mega-Pascals and two thousand mega-Pascals, wherein a one millimeter thickness of the body has an optical transmittance of between twenty percent and ninety-five percent for a wavelength of light that is between four hundred nanometers and seven hundred nanometers.
In one embodiment, a dental device is disclosed comprising a solid body including at least eighty mass percent dental ceramic molecules in the form of crystals having a length and a width such that an aspect ratio of the length to the width is at least two to one, the body having a shape of a dental prosthesis, having a flexural strength that is between six hundred mega-Pascals and two thousand mega-Pascals, wherein a one millimeter thickness of the body has an optical transmittance of between twenty percent and ninety-five percent for a wavelength of light that is between four hundred nanometers and seven hundred nanometers.
In one embodiment, a dental device is disclosed comprising a solid body containing at least forty atomic percent tetragonal zirconium oxide crystals having a mean size of between one nanometer and one hundred nanometers, and a standard deviation from the mean size that is less than twenty percent of the mean size, the body shaped in the form of a dental prosthesis and characterized by having a flexural strength between eight hundred mega-Pascals and two thousand mega-Pascals, and having an optical transmittance for a one millimeter thickness of between thirty-five percent and ninety-five percent for a wavelength of light that is between four hundred nanometers and seven hundred nanometers.
In one embodiment, a dental device is disclosed comprising a solid body containing at least forty mass percent tetragonal zirconia in the form of crystals having a length and a width such that the length is at least twice as large as the width, the body shaped in the form of a dental prosthesis and characterized by having a flexural strength between eight hundred mega-Pascals and two thousand mega-Pascals, and having an optical transmittance for a one millimeter thickness of between thirty-five percent and ninety-five percent for a wavelength of light that is between four hundred nanometers and seven hundred nanometers.
In one embodiment, a dental device is disclosed comprising a solid body made of a compressed powder containing at least forty mass percent tetragonal zirconia, the body shaped in the form of a dental blank and having a density that is between thirty percent and eighty percent of a theoretical maximum density of the body, wherein the powder is made of particles having a mean size in a range between one-half nanometer and thirty nanometers, and a standard deviation from the mean size that is less than twenty percent of the mean size.
In one embodiment, a dental device is disclosed comprising a solid body made of a compressed powder containing at least eighty mass percent tetragonal zirconia, the body shaped in the form of a dental blank, the powder made of particles having a maximum size of twenty nanometers.
In one embodiment, a dental device is disclosed comprising a solid body made of a compressed powder of dental ceramic particles, wherein the dental ceramic particles include zirconium oxide, aluminum oxide, hafnium oxide, niobium oxide or yttrium oxide, the body shaped in the form of a dental blank and the particles having a mean size of between one-half nanometer and ten nanometers, and a standard deviation from the mean size that is less than twenty percent of the mean size.
In one embodiment, a dental device is disclosed comprising a solid body made of a compressed powder containing dental ceramic nanorods, the body shaped in the form of a dental blank and characterized by having a density that is between thirty percent and eighty percent of a theoretical maximum density of the body.
In one embodiment, a dental device is disclosed comprising a solid body made of a compressed powder containing at least eighty mass percent dental ceramic particles having a length to width aspect ratio of at least two to one, the body shaped in the form of a dental blank and characterized by having a density that is between forty percent and eighty percent of a theoretical maximum density of the body.
In one embodiment, a dental device is disclosed comprising a bisque-state solid body containing at least eighty mass percent tetragonal zirconium oxide crystals having a mean size of between one nanometer and one fifty nanometers, and a standard deviation from the mean size that is less than twenty percent of the mean size, the body shaped in the form of a dental blank and having a density that is between fifty percent and ninety percent of a theoretical maximum density of the body.
In one embodiment, a dental device is disclosed comprising a bisque-state solid body containing at least eighty mass percent tetragonal zirconium oxide crystals having a length to width aspect ratio of at least two to one, the body shaped in the form of a dental blank and having a density that is between fifty percent and ninety percent of a theoretical maximum density of the body.
In one embodiment, a dental device is disclosed comprising a bisque-state solid body made of dental ceramic crystals containing at least fifty mass percent zirconium oxide, aluminum oxide, hafnium oxide, tantalum oxide, titanium oxide, niobium oxide, or yttrium oxide having a length to width aspect ratio of at least two to one, the body shaped in the form of a dental blank and having a density that is between fifty percent and ninety percent of a theoretical maximum density of the body.
In one embodiment, a dental device is disclosed comprising a solid body made of a powder mixed with a binder, the body shaped in the form of a dental blank, the powder containing at least forty mass percent tetragonal zirconia, wherein the powder is made of particles having a mean size in a range between one-half nanometer and thirty nanometers, and a standard deviation from the mean size that is less than twenty percent of the mean size.
In one embodiment, a dental device is disclosed comprising a solid body made of a powder mixed with a binder, the body shaped in the form of a dental blank, the powder containing at least eighty mass percent tetragonal zirconia, the powder made of particles having a maximum size of twenty nanometers.
In one embodiment, a dental device is disclosed comprising a solid body made of a powder mixed with a binder, the body shaped in the form of a dental blank, the powder made of dental ceramic particles, wherein the dental ceramic particles include zirconium oxide, aluminum oxide, hafnium oxide, niobium oxide or yttrium oxide, and the dental ceramic particles have a mean size of between one-half nanometer and ten nanometers, with a standard deviation from the mean size that is less than twenty percent of the mean size.
In one embodiment, a dental device is disclosed comprising a solid body made of a powder mixed with a binder, the powder containing dental ceramic nanorods, the body shaped in the form of a dental blank and having a density that is between twenty percent and seventy percent of a theoretical maximum density of the body.
In one embodiment, a dental device is disclosed comprising a solid body made of a powder mixed with a binder, the powder containing at least eighty mass percent dental ceramic particles having a length to width aspect ratio of at least two to one, the body shaped in the form of a dental blank and having a density that is between twenty percent and seventy percent of a theoretical maximum density of the body.
In one embodiment, a method for making a dental device is disclosed comprising: forming a vapor containing dental ceramic particles of at least one oxide, nitride, carbide, oxy-nitride or carbon-nitride of zirconium, hafnium, aluminum, niobium, tantalum, titanium or yttrium; collecting the dental ceramic particles as a powder having a maximum particle diameter of between one nanometer and ten nanometers; and forming the powder into a dental blank. In one embodiment, the method for making a dental device further comprises forming the blank into a shape of a dental prosthesis. In one embodiment, the method for making a dental device further comprises sintering the prosthesis.